The present invention relates to improvements in aspirators for withdrawal of secretions from wounds and for analogous purposes. More particularly, the invention relates to improvements in aspirators of the type wherein a bottle or another suitable vessel has an inlet for attachment of a needle or cannula which can draw secretions from wounds or from cavities of animal bodies due to the pressure differential between the interior of the vessel and the surrounding atmosphere.
Aspirators of the above outlined character can be employed postoperatively for withdrawal of secretions from wounds which are the result of injury or surgery as well as for adaptation of the surfaces bounding the wounds, normally for a period of several (for example, three) days following the operation. As a rule, or at least in many instances, the aspirator comprises a rigid or substantially rigid vessel from which air is withdrawn so that the subatmospheric pressure in its interior is supposed to equal or approximate a preselected value. The vessel is normally of the dispensable type, i.e., it is discarded after a single use, and its inlet is connected to a needle or cannula by way of which secretions are drained from the wound and/or by way of which the wound is drained by suction.
An aspirator of the just outlined character is disclosed, for example, in German Auslegeschrift No. 28 20 517. This asp:rator is provided with a pressure indicator which is located at the top of the vessel and whose primary purpose is to indicate whether or not the aspirator is ready for use. In other words, the indicator serves to furnish information denoting to the patient, to the nurse or to the physician that the pressure in the interior of the vessel is below atmospheric pressure, i.e., that the vessel is ready to draw secretions by way of a needle, a cannula or an analogous implement.
In certain presently known aspirators, the means for indicating the pressure in the interior of the vessel include bellows, elastically deformable membranes or reciprocable plungers which can be observed from the outside and whose position relative to a scale or the like denotes the pressure prevailing in the interior of the vessel. A drawback of such pressure indicating devices is that their mobile parts are likely to jam and/or adhere to the adjacent portion of the vessel due to accumulation of condensate in the interior of the vessel and/or as a result of contamination by secretions. Moreover, known indicating devices are merely designed to denote the presence or absence of suction but not the exact subatmospheric pressure (if any) which prevails in the interior of the vessel. In other words, a person observing the position of the bellows, membrane or plunger will merely ascertain that the interior of the vessel is or is not maintained at less than atmospheric pressure but the exact pressure cannot be ascertained at all. Therefore, such person is not in a position to determine whether or not the initial pressure (prior to admission of any secretions into the vessel) matches or approaches the prescribed or optimum value, i.e., whether or not the vessel is indeed capable of accumulating a certain quantity of secretions.
The ability of the aspirator to accumulate secretions depends entirely on the subatmospheric pressure which prevails in the interior of the vessel prior to admission of secretions. Once the pressure has risen to a certain level, the vessel is incapable of drawing additional secretions, i.e., the secretions accumulate in the wound and are likely to cause an enlargement of the wound, hematoma and/or other undesirable phenomena. Moreover, the adaptation of the region surrounding the wound is terminated or interrupted which can lead to infection of the wound. Thus, the inability of a conventional aspirator to indicate whether or not the vessel is capable of accepting additional secretions and/or the maximum quantity of secretions which can be gathered in the vessel constitutes a serious drawback which can have grave consequences if the condition of the aspirator is not monitored continuously or at frequent intervals. The person in charge cannot rely simply on superficial visual observation of the contents of the vessel since the vessel cannot be filled to capacity but rather only as long as the subatmospheric pressure therein is within a certain range, i.e., the secretions can fill only a certain percentage of the overall volume of the vessel.